1. Field of the Invention
The invention is an improved one-piece, hollow bicycle wheel rim having improved sectional shape and surface for high performance caliper braking and composite layup providing lighter weight and increased strength in an economical manner.
2. Description of Related Art
Basic principles of optimum compaction low void composite molding the bicycle industry are described in U.S. Pat. Nos. 5,624,519 and 6,270,104, sharing a common assignee with this application. The disclosures in U.S. Pat. Nos. 5,624,519 and 6,270,104 are incorporated by reference as if fully set forth herein. It will be noted that the fiber/resin areal ratios taught in those patents correspond to a fiber to resin ratio of about 65/35 by weight.
Metal wheel rims have long been made by bending a straight extrusion, bar or other shape to a circular form and then joining the ends to make a closed circle. It is also known to machine a brake surface, particularly after welding an aluminum rim, as in European Patent Office Publication No. 0579525A1. These patents and publications are incorporated by reference as fully set forth herein.
Owing to the different strength, and coefficient of friction properties of composite fiber reinforced plastics, particularly the high tensile strength and high stiffness of materials such as carbon fiber, the base material is formed to shape prior to curing However there has long been a concern about the performance of such structurally sound rims under high performance caliper braking conditions, such as in a long, fast descent on a mountain road.
Three typical methods of forming a wheel. or wheel rim from carbon fiber reinforced plastic are known in the prior art. The first of these is a cored composite in which the high strength skin surrounds a core such a foam core, U.S. Pat. No. 5,061,013. The second is a solid composite such as U.S. Pat. No. 6,347,839 B1 in which composite laminations have no designed end openings or different density materials between interior and exterior surfaces. The third prior art approach is a partially hollow but plugged construction such as U.S. Pat. No. 6,398,313 B1 where two hollow halves have interior inserts and exterior reinforcements at joining ends. The disclosures in these three patents are incorporated by reference as if fully set forth herein. U.S. Pat. No. 6,991,300, which issued from an application that had been copending with the present application, discloses use of optimum compaction, low void manufacturing for an aerodynamic section, two piece rim. The disclosure therein is incorporated by reference herein.
The segmented arrangement used in the invention improves on the prior art such as Lew U.S. Pat. Nos. 6,347,839 or 6,398,313 by using general principles of optimum compaction low void composite construction specially adapted to the unique shape and structural requirements of high braking performance and light weight wheel rims using a combination of laminates incorporating fibers at different angles relative to one another.
Notably, unlike prior art carbon fiber wheel or rim forming techniques, the instant rims are formed from a plurality of prepreg segments, tabbed to overlap to result in a solid wall, but hollow rim. Preferably six segments per side, for a total of twelve, are formed surrounding a bladder, with overlapping tabs on each side and at the center plane, such that under curing pressure and temperature there is a continuous chemical bond in the preferred epoxy matrix. Six segments per side better aligns the fibers with expected loads when the preferred 0-45-90 degree oriented fiber layups are used. The segments are staggered from side to side so that seams on one side do not line up transversely across from seams on the other side.
The molds contain plugs or projections to form spoke nipple access holes and enabling precise alignment of the spoke hole finishing tools. The valve stem hole can also be provided for in this manner.
After forming the uncured skin, the unit is placed in a mold, the mold closed, the bladder pressurized while the mold is heated. When fully cured, the rim is removed from an opened mold and the bladder removed. Finishing of the access holes and spoke holes is accomplished and, if desired, the brake walls may be further machined.
The preferred carbon fiber reinforced epoxy laminate structure has a tough, high performance braking surface, which may also be made machinable.